Key Highlights

  • Sunstone has received all outstanding assays from its 2026 surface-sampling programme at Porotillo.
  • Porotillo is a gold-copper porphyry system within the Bramaderos project in southern Ecuador.
  • The final batch covers trenches PO-10 to PO-17 and channel sample PC5.
  • Grades of around half a gram per tonne gold equivalent are modest in isolation, with their significance in breadth.

Sunstone Metals (ASX:STM) has received all outstanding assays from its 2026 surface-sampling programme at Porotillo, a gold-copper porphyry system within the Bramaderos project in southern Ecuador. The final batch covers trenches PO-10 to PO-17 and channel sample PC5, and was reported to the ASX on 4 November.

The widest new interval came from trench PO-16a, which returned 126.32 metres at 0.41 grams per tonne gold equivalent. PO-15 delivered 95.50 metres at 0.50 g/t AuEq, PO-10c 97.58 metres at 0.44 g/t and PO-10d 89.56 metres at 0.47 g/t. The highest average grade among the new lines was 30.38 metres at 0.64 g/t AuEq in PO-10b.

Reading the numbers correctly

These are trench lengths measured along the surface, not drill intercepts, and true widths are unknown. Sunstone states that the data do not contribute to any resource estimate and do not imply grade continuity. Results from separate trench lines have not been combined.

Grades of around half a gram per tonne equivalent are modest in isolation. Their significance lies in breadth: porphyry deposits are typically bulk, lower-grade systems where long continuous mineralised intervals matter more than spectacular individual assays. The gold-equivalent calculation uses prices of US$3,000 an ounce for gold, US$6.0 a pound for copper and US$40 an ounce for silver, with assumed recoveries of 91%, 78% and 60% respectively.

Mineralisation is hosted mainly in quartz diorite and intrusive breccia, with vein types and magnetite that Sunstone regards as consistent with a porphyry-style system.

The reported trenches are spread across the target. PO-10 and PO-16 sit in the west and north, PO-15 in the centre, and PO-11 to PO-13 in the south-east and south. That distribution matters because it tests the surface footprint in several directions rather than repeatedly sampling one favourable spot.

Why trenching has mattered before

Porotillo shows how the company uses surface work. The 17-trench programme was completed in stages between December 2025 and September 2026; an earlier trench, PO-5, returned 462.22 metres at 0.55 g/t AuEq. A 20-hole, 3,866-metre diamond programme over those trench targets then led to the Porotillo discovery, which was included in the October 2026 Mineral Resource Estimate alongside Copete.

That estimate lifted Bramaderos by 72% to 464 million tonnes at 0.42 g/t AuEq for 6.2 million ounces, comprising 229 million tonnes Indicated at 0.45 g/t and 236 million tonnes Inferred at 0.38 g/t. Sunstone says the latest trench results suggest the Porotillo system may extend beyond the area tested by drilling.

Managing director Patrick Duffy pointed to an Exploration Target of 4.4 to 11.2 million ounces AuEq in addition to the resource. That target is conceptual; there has been insufficient exploration to estimate a resource for it, and it may never become one.

Ownership and funding questions

The Bramaderos concession is held in a joint venture in which Sunstone owns 87.5% and Jiangxi Copper 12.5%. Sunstone is also running a strategic process to determine a preferred long-term funding model for its two projects. For a company of its size, how a large, low-grade porphyry would eventually be financed is as important as further geological growth.

Next steps

Sunstone has flagged three follow-up areas: extensions south and west of the pit-constrained Porotillo resource; strong copper-in-soil anomalies above 800 parts per million south of Porotillo Hill, where short reconnaissance trenches are being assessed; and eight trenches totalling about 844 metres now underway between Copete and Melonal along a 650-metre trend.

No firm dates were given for these. Results from Copete-Melonal will be released once that programme is completed and interpreted, and the new assays will be combined with drilling, mapping and geophysics to refine future drill targets. Investors should watch whether subsequent drilling converts these broad surface intervals into additional resource ounces.